If you feed a layer type pellet or crumble feed, you don't really need to offer oyster shell on the side but you can.I was thinking about laying pellets.
What do you think pellets and oysters shells will do?
The reason the feed contains the word layer is because it already has enough calcium in it for a laying bird.
If you were to buy a chick type crumbled feed, then you would need to offer the oyster shell on the side because it does not contain enough calcium for a laying bird.
Whichever feed you buy, make sure that it is a crumbled or pelleted type feed and not a whole grain or mixed seed stuff.
Offering a seed mix or a whole grain mix. Gives the bird an option to pick and choose which seed or grade it wants to eat and it will not get a balanced diet which will cause problems.